Beta-decay rates of FP shell nuclei with A greater than 60 in massive stars at the presupernova stage

Details Beta-decay rates of FP shell nuclei with A greater than 60 in massive stars at the presupernova stage Beta-decay rates of FP shell nuclei with A greater than 60 in massive stars at the presupernova stage

Oct 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...434..662k&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 434, no. 2, p. 662-683

Other

28

Abundance, Beta Particles, Cobalt Isotopes, Copper Isotopes, Decay Rates, Electron Capture, Massive Stars, Stellar Cores, Stellar Models, Supernovae, Nuclear Fission, Nuclear Fusion, Spectral Energy Distribution, Stellar Evolution

Scientific paper

Beta decay and electron capture on a number of neutron-rich nuclei with A greater than 60 at the presupernova stage may play an important role in determining the hydrostatic core structure of massive presupernova stars and, through this, affect the subsequent evolution during the gravitational collapse and supernova explosion phases. In particular, some isotopes of cobalt and copper can make a substantial contribution to the overall changes in the lepton fraction and entropy of the stellar core during its very late stage of evolution. In the stellar evolution calculations to date, many of these nuclei could not be appropriately tracked in the reaction network, since reliable rates for these have not been available so far. We describe a model to calculate the beta-decay rates using an average beta strength function and an electron phase-space factor evaluated for typical presupernova matter density (rho = 3 x 107-3 x 109 g/cu cm) and temperature (T = (2-5) x 109 K). For the Gamnow-Teller (GT) strength function we use a sum rule calculated by the spectral distribution theory, and the centroid of the distribution is obtained from experimental data on (p, n) reactions. The width sigma of the GT strength function has two parts (sigma2 = (sigmaN exp 2 + (sigmaC exp 2, with sigmaC = 0.157ZA-1/3). The parameter sigmaN is fixed by a best fit to the observed half-lives for the free decays of a number of A greater than 60 nuclei. In the calculation of rates we include contributions from the excited states of the mother nucleus wherever they are known experimentally. For the excited states one uses the same form of the GT strength function, but shifted in energy using the extended isobaric analog state argument. The method is particularly suited for calculating contributions from the excited states important at high temperatures relevant at the presupernova stellar evolution phase. We also include the contributions to the transition rates from the Gamow-Teller resonance states (e.g., the GTR+ state) in the mother nucleus, which may be thermally populated. The beta-decay rates for nuclei having A greater than 60 reported here can be inputs for presupernova stellar evolution and nucleosynthesis calculations employing detailed nuclear reaction networks relevant in the advanced phases of hydrostatic nuclear burning.

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